Diapers and like sheetlike materials



Patented Nov. 1, 1949 DIAPERS AND LIKE SHEETLIKE MATERIALS Raymond B.Seymour and George M. Schroder, Chattanooga, Tenn., assignors to HenryH. Frede and Company, Chattanooga, Tom a corporation of Tennessee NoDrawing. Application October 8, 1947, Serial No. 778,717

8 Claims. 1 This invention relates to diapersand sheets and moreparticularly to articles of this character which may be disposed ofafter a single use.

There is a considerable demand for disposable diapers because of theconvenience of their use.

: As they are discarded after they have been used once, they completelyeliminate the objectionable handling and washing of soiled diapers. Theyhave the added advantage that it is generally unnecessary to have onhand as many disposable diapers as would be required of the customarycloth diapers which are reused.

Despite the acknowledged benefits of disposable diapers the ones nowavailable have not had complete public acceptance because of certainundesirable properties. They have either been expensive or they havelacked the qualities requisite of a satisfactory diaper. If they havehad desirable physical properties, they have been costly to manufactureand their consequent high selling price has limited their sales.

The disposable diapers which have been sold at an acceptable low pricehave not been satisfactory because they have not been sufficiently absorptive or have been so bulky or harsh in texture that their use hasbeen avoided. They frequently have formed wrinkles and creases whenfolded about the infant and consequently lack the desired smoothness.Or, their surfaces have been of such a coarse or rough material thatthey have chafed the infants skin.

These objectionable properties of the prior disposable diapers havearisen because a satisfactory diaper presents a somewhat conflicting setof conditions. It is of course preferable that it be thin so that itwill not be bulky, but this requires that it have exceptional absorptioncapacity. Also, if it is thin it must be highly absorptive on one sideand be water repellent on its other side. In addition it must be strongeven when wet and this is especially difficult toobtain in a thindiaper. The diaper of the present invention can be made at low cost. Itis thin and therefore it is not bulky when applied to the infant; it issoft and therefore does not chafe when wrinkled and creased; Despite itsthinness it has a satisfactory strength even when wet and has a highabsorptive capacity. It is made water repellent on one side by amoisture resistant coating, but this does not detract from either thehighly pliable character of the product or from its soft and smoothtexture. I

Generally considered, the diaper of the invention consists of a basematerial which is a sheet of loose, unwoven fibers having a randomdistribution. To one side of this fibrous sheet is applied a coatingwhich retains the surface fibers against movement but which readilyabsorbs and transmits moisture to the inner fibers. To the other side ofthe fibrous sheet is applied a coating which serves as a binder for thesurface fibers. and also serves as a water proofing material.

The fibrous sheeting employed to carry out the invention is preferablythat obtained by garnetting picked, woven, knitted or felted materialsof virgin cotton or other cellulosic fibrous materials In this process,an especially designed machine of known type called a picker picks apartthe woven, knitted or felted materials and these materials, virgincotton, viscose rayon, or other cellulosic fibrous materials, are formedinto a batting or felt of substantially uniform thickness of anespecially designed machine of known type called a garnett. This fibroussheet is economically produced, particularly if it is made from waste orrejected cellulosic or wool cloth. The cellulosic fibers may be eithernatural or synthetic.

The resulting sheet of fibrous material has the advantage over felt orbatting produced by a carding process because its fibers are distributedin all directions in a random fashion. The fibrous sheet consequentlyhas substantially no tensile strength in any direction, but whatstrength it does possess is nearly uniform in all directions due to theirregular disposition of the fibers. This would not be true of a cardedfelt as there the fibers are all lined up in the same direction.

To one side of this sheet of fibrous material is applied the materialwhich is to form the coating which is to bind the surface fiberstogether and also transmit moisture to the interior of the felt.Although the sheet of irregularly arranged fibers is weak, it hassufiicient strength to be handled during application of this fiberbinding material.

One suitable coating material for this purpose is applied as a diluteaqueous solution of a sodium salt of carboxy methyl cellulose and thismay, for example, be a sodium salt of an ether formed by the reaction ofalkali cellulose and monochloro acetic acid in such manner as to obtaina product having from 0.2 to 1.0 glycolate groups per anhydro glucoseunit of cellulose at a pH of 3 to 8.5. One suitable product of thischaracter is that having a molecular weight such that a 2% aqueoussolution will have a viscosity of from 10 to 1,000 centipoises. It ispreferable to employ a medium molecular weight of the cellulose ether i.l. A... l wwmnwwanah.

derivative, but a blendof high and low molecular weight products may beused.

A preferred dilution of the sodium salt of carboxy methyl cellulose forapplication to the fibrous sheet, is a 1% aqueous solution. Excelbybringing the fibrous sheet into contact with a rotating roller uponwhich the solution is continuously sprayed. A film of the solution isthereby formed upon the roller and this film is transferred to thefibrous sheet as the sheet continuously comes into contact with therotating roller.

After a film of the aqueous solution of the cellulose derivative isapplied to the fibrous sheet, heat is applied to remove the water ofsolution. This heat is preferably applied by advancing the coated sheetto a rotating roller maintained at a temperature of from 300 to 450 F.This heated roller also serves to drive the coating material into thesurface of the fibrous sheet.

It is important to heat the coating film to a temperature of from 300 to450 F. to obtain the full benefits of the use of this substance. Byapplying this moderately high heat the cellulose derivative becomesquite water insoluble but does not lose its capacity'to absorb moisture.It is not definitely known why this heat changes the water solublecompound to an essentially water insoluble compound but one explanationis that the carboxyl group on the carboxymethyl cellulose reacts with afree hydroxyl group in an adjacent carboxymethyl cellulose molecule toform a compound having an apparent high molecular weight. This result isnot obtained if heat of only 250 F. is applied. 7

It is preferable that the cellulose derivative be applied in suchquantity that it will be present in the range of from 0.1 to 0.4 poundper thousand square feet. This film thickness may be obtained byproperly relating the quantity of coating material being delivered bythe spray to the speed of travel of the fibrous sheet.

As a result of the application of this coating to one side of thefibrous sheet, the portions of the fibers at the surface are heldagainst relative movement. The water absorbability of the fibers is notimpaired as the water rapidly penetrates through the coating. Due to theformation of a substantially continuous film of the binding material,all, or nearly all of the surface fiber portions are interconnected bothat their points of intersection and along their intervening sections.Also, as the binding material penetrates somewhat into the sheet, itbinds together the fibers below the surface.

Although the solution of the sodium salt of carboxy methyl cellulose.which has been described, is a preferred coating material, the inventioncan be practiced by employing other materials which will form a coatingwhich will bind. the surface fibers against relative movement and whichwill transmit moisture through the coating to the inner fibers of thesheet. One such material which can be employed is hydroxy ethylcellulose.

This coatingmaterial is applied in much the same way as the sodium saltof carboxy methyl cellulose. In this application there must besufficient hydroxyethyl groups present to permit the product to besoluble in aqueous alkali. Those cellulose derivatives having additionalhydroxyethyl groups are also satisfactory. These materials are preparedby reacting aqueous solutions of alkali cellulose with ethylene oxide attemperatures ranging from 10 to 60 C. and both the alkali soluble andwater soluble types are commercially available.

A preferred dilution o hydroxyethyl cellulose is a 2% aqueous solutionbut excellent results are obtained with aqueous solutions of 0.5 to 5%.

The method of application is essentially the same as that used in theprevious example. However. it has been found advantageous to dry thefibrous sheet impregnated with hydroxyethyl cellulose at about 220 F.before subjecting it to the elethis material is essentially imperviousto water.

A preferred proportion is to have the styrenemaleic anhydride constituteof the combined weight.

The hetero-polymer of styrene and maleic acid may be obtained, forexample. in accordance with the disclosure of Patent 2,047,398 to Vosset al. and it should have a molecular weight such that a 0.2% aqueoussolution will have a viscosity of from 0.5 to 50 centipoises. Theammonium salt of this polymer is used in making up the aqueous solutionfor application to the fibrous sheet. This aqueous solution alsocontains a solid polyethylene glycol and these solid polyethyleneglycols may vary in average molecular weight from 1000 to 7000. Thesematerials are very water-soluble and are highly hygroscopic.

It may be observed that to obtain the waterrepellent coating, someconsideration should be given to the molecular weight of the solidpolyethylene glycol. Thus, with the lower molecular weights, it ispossible to obtain a water-repellent coating by use of largerproportions of solid polyethylene glycol than in the case when highermolecular weight polyethylene glycol is used.

Preferably, the solid polyethylene glycol and the styrene-maleicanhydride, in the above range of proportions, are used in an amount tomake up a 1% aqueous solution. Excellent results are however obtainedwith an aqueous solution of from 0.5 to 4.0%. This aqueous solution maybe applied in the same manner that the solution of the sodium carboxymethyl cellulose is applied to the other side of the fibrous sheet, asdescribed above. This involves the use of an applying roller upon whichthe solution is sprayed, and a heated roller maintained at a temperatureof from 250 to 450 F.

The heated roller not only serves to remove the water of solution, butalso serves to drive oil the' ammonia from its salt of thestyrene-maleic anhydride. As a result, a water repellent coating mo'niais driven ofl. Since only two hydroxyl groups are present in moleculesof the polyethylene glycol having molecular weights of 1000 to 7000, itis surprising that a soft flexible film which is essentially insoluble,results. v

This coating of solid polyethylene glycol and styrene-maleic acid, likethe coating, for example, of sodium carboxy methyl cellulose 0n theother side of the fibrous sheet, is continuous or substantiallycontinuous. As a consequence, all, or practically all of the fiberportions at the surfaces are retained in these coatings and thereby heldagainst displacement. It is this structure, as distinct from a structurein which the binding material is localized at the intersections of thefibers, which accounts for the high strength of the present product. Astrong interconnection exists between the fibers not only at theirsurface points of intersection but along their intervening portions atthe surface of the sheet, aswell.

It is preferable that the mixture of the solid polyethylene glycol andthe styrene-maleic anhydride be applied in such quantity that it will bepresent in the range of 0.25 to 2.0 pounds per thousand square feet. Afilm of corresponding thickness can be readily applied by adjusting thespeed of rotation of the applying roller and the quantity delivered bythe spray.

As has been noted, the coating of sodium carboxy methyl cellulose orother material having a like function on the one side of the fibroussheet, is water absorptive and freely transmits it to the inner fibers,and this makes it possible to deposit this as a continuous film. Thecoating of the solid polyethylene glycol and styrenemalelc anhydride, ishowever water resistant and not only serves to bind the fibers butproduces a water resistant barrier.

In its broader aspects, therefore, the invention involves a sheet ofunwoven fibers having a random distribution, on one side of which is theinterpolymer of solid polyethylene glyocol and styrene-maleic acid toproduce a water-repellant coating, andon the other side of which is acoating which will bind together the surface fibers and transmitmoisture to the interior fibers of the sheet. Because of the highstrength of the water-repellent coating which has been described it isnot absolutely essential that the coating on the other side impart ahigh strength to the sheet.

By using this coating of solid polyethylene glycol, and styrene-maleicacid interpolymer, a highly satisfactory water-proofing coating isformed. It performs a two-fold function as has been noted, thus makingit unnecessary to add an additional water-proofing coating. The coatingis flexible and will not crack when bent, it

is not tacky, and it presents a smooth surface which is not unpleasant.Moreover, it has no deleteriousefiect on the infants skin. It acts as abarrier to prevent the passage of absorbed water through thematerial butdoes not impair the absorbalbility of the fibrous sheet.

' Th resulting diaper not only possesses this considerable capacity toabsorb moisture, but it retains considerable strength even afterbecoming wet. As a consequence, safety pins used to hold the diaper inplace, will not pull through the material after it becomes wet. As hasbeen stated. because the diaper is thin it can easily be folded in placeand does not form objectionable creases and It is soft and flexible andis no more annoying to the infant than cloth diapers.

Although the invention has been described with particular reference todiapers, it is to be understood that the product of this invention maybe applied to equivalent uses. Thus, the sheet material of the inventionmay be used in situations where its absorbent properties are desired,such as for bibs, table cloths, surgical sheets, and the like.

The invention may be further illustrated by the following examples:

Example 1.Rejected cotton cloth is picked apart in a picker and feltedin a garnetting machine and the resulting felt having a weight of 1 to 2ounces per running yard is sprayed on one side of the garnetted materialwith a 2% aqueous solution of sodium carboxy methyl cellulose. The otherside is sprayed with a 2% aqueous solution made up of 0.6 pound ofdissolved solid polyethylene glycol having an average molecular weightof 1540, and 1.4 pounds of the ammonium salt of styrene-maleic acid in98 pounds of water. The treated material is passedthrough drum rollersto dry the coatings. The roll drying the water absorptive carboxy methylcellulose film has a temperature of 400 to 420 F., while the other rollused to remove the water from the polyethylene glycol styrene-maleicanhydride has a temperature of 400 to 450 F. The resulting sheet is cutto a trapezoidal shape.

Example 2.Discarded viscose rayon and cotton cloth are picked apartsimultaneously on pickers, the materials are conveyed to difierentgarnetting machines and the products from these materials are conveyedto a common apron so that the long, staple, soft rayon forms one surfaceof the garnetted sheet. This sheet is coated as in Example 1, thewater-proofing coating being applied to the cotton side.

Example 3.--Virgin cotton is used instead of picked and garnetted clothas in Example 1.

Example 4.-To garnetted cotton fiber in mat form is applied on one sidea 2% aqueous solution of hydroxyethyl cellulose and on the other side isapplied a 2% aqueous solution of solid polyethylene glycol having anaverage molecular weight of 4000 and an ammonium salt of styrene maleicacid using a ratio of 67.5 to 22.5.

The impregnated batting is dried at 210 to 230 F. and then passedthrough rolls at 375 to 450 F. The product is cut and placed inpackages.

Diapers made in accordance with this invention possess excellentproperties as shown by the following tests:

A piece of felt 1" in cross section and processed according to Examplel,was placed between clamps and weights were added and the length oftime i for break was determined, the distance between the clamps being2". The untreated felt broke immediately when a 20 gram weight wasadded. The treated product was not broken in 10 seconds after theaddition of a 1500 gram weight. The sample was immersed in water and thetest was repeated. Under these conditions the sample did not break in 10seconds after the addition of the 1500 gram weight. The tests wererepeated using strips cut at right angles to the previously describedtest pieces, and under these conditions similar results were obtained.

A piece of bonded cotton felt, measuring 3" x 4" and weighing 1 gram,was immersed in water for 10 seconds, placed on blotting paper for 5seconds and reweighed. The total weight after this procedure was 11grams, indicating that the material had absorbed times its own weight ofwater. This test was repeated using a piece or absorbent woven clothweighing 1 gram and the woven material gained 4 grams'in weight due tothe absorption of water.

A section of the diaper type material was clamped to a glass cylinder inwhich was placed 50 ml. water, the column of water being 6 centimetersabove the coated cloth. At the end oi} ten minutes no water had passedthrough the material.

What is claimed is:

l. A diaper having one side water-repellant comprising a sheet ofunwoven fibers having a random distribution, a substantially continuousmoisture transmitting coating on one side thereof of sodium carboxymethyl cellulose having a thickness corresponding to from 0.1 to 0.4pound per thousand square feet and which has been rendered essentiallywater-insoluble by heat treatment to a temperature of from 300 to 450F., and on the other side of the fibrous sheet, a water-repellentcoating of a water insolubilized composition consisting f 25 to 40 partsof a solid polyethylene glycol having an average molecular weight of1000 to 7000 and 60 to 75 parts of a styrene-maleic anhydrideinterpolymer, the latter coating having been subjected to a temperatureof from 250 to 450 F. l

2. A diaper having one side water-repellent comprising a sheet ofunwoven fibers having a random distribution, a substantially continuousmoisture transmitting coating on one side thereof of sodium carboxymethyl cellulose which has been rendered essentially water-insoluble byheat treatment to a temperature 01 from 300 to 450 F., and on the otherside of the fibrous sheet, a water-repellent coating of a waterinsolubilized composition consisting of 25 to 40 parts of a solidpolyethylene glycol having an average molecular weight of 1000 to 7000and to 75 parts of a styrene-maleic anhydride interpolymer, the lattercoating having been subjected to a temperature of from 250 to 450 F. andhaving a thickness corresponding to from 0.25 to 2.0 pounds per thousandsquare feet.

3. A diaper having one side water-repellan comprising a sheet of unwovenfibers having a random distribution, a substantially continuousmoisture-transmitting coating on one side thereof of sodium carboxymethyl cellulose which has been subjected to a temperature of from 300to 450 F., and on the other side of the fibrous sheet, a water-repellentcoating of a composition consisting of 25 to 40 parts of a solidpolyethylene glycol having an average molecular weight of 1000 to 7000and 60 to '75 parts of a styrenemaleic anhydrlde interpolymer, saidcomposition having been subjected to a temperature of from 250 to 450 F.

4. A diaper having one side water-repellant comprisin a sheet of unwovenfibers having a random distribution, a substantially continuous moisturetransmitting coating on one side thereof of sodium carboxy methylcellulose which has been subjected to a temperature of from 300 to 450F., said coating having a thickness corresponding to from 0.1 to 0.4pound per thousand square feet, and on the other side of the fibroussheet, a water-repellant coating of a composition consisting of 25 to 40parts of a solid polyethylene glycol having an average molecular weightof 1000 to 7000 and 60 to 75 parts of a styrenemalelc anhydrldeinterpolymer, said composition having been subjected to a temperature offrom 250 to 450 F., the latter coating having a thickness correspondingto from .25 to 2.0 pounds per thousand square feet.

5. A diaper having one side water-repellent comprising a sheet ofunwoven fibers having a random distribution, a substantiall continuousmoisture transmitting coating on one side thereof of sodium carboxymethyl cellulose having a medium molecular weight and which has beensubjected to a temperature of from 300 to 450 F., and on the other sideof the fibrous sheet, a water-repellant coating of a compositionconsisting of 25 to 40 parts of a solid polyethylen glycol having anaverage molecular weight of from 1,000 to 7,000, and 60 to '75 parts ofa styrene-maleic anhydride interpolymer having a molecular weight suchthat a 0.2% aqueous solution will have a viscosity of from 0.5 to 50centipolses, the latter coating having been subjected to a temperatureof from 250 to 450 F. to render it substantf ally water insoluble.

6. The process of making a diaper having one side water-repellant whichcomprises applying to one side ofa sheet of unwoven fibers having arandom distribution, a substantially continuous coating of a 0.5 to 2.0%aqueous solution of sodium carboxy methyl cellulose, applyin heat tosaid coating on the order of 300 to 450 F. whereby a moisturetransmitting coating is obtained, applying to the other side of thesheet a substantially continuous coating of a 0.5 to 4.0% aqueous.solution of 25 to 40 parts of a solid polyethylene glycol having anaverage molecular weight of 1000 to 7000 and .60 to parts of an ammoniumsalt of styrene-maleic anhydride interpolymer, and applying heat to thelatter coating on the order of 250 to 450 F, to expel the water ofsolution and convert the coating to an essentially water insoluble andwater-repellant product.

I. The process of making a diaper having one side water-repellent whichcomprises applying to one side of a sheet of unwoven fibers having arandom distribution, a substantially continuous coating of a 0.5 to 2.0%aqueous solution of sodium carboxy methyl cellulose, applying heat tosaid coating on the order of 300 to 450 F. whereby a moisturetransmitting coating is obtained, applying to the other side of thesheet a substantially continuous coating of a 0.5 to 4.0% aqueoussolution of 25 to 40 parts of solid polyethylene glycol having anaverage molecular weight of 1000 to 7000 and 60 to '75 parts of anammonium salt of styrene-maleic anhydride interpolymer, and applyingheat to the latter coating on the order of 300 to 450 F. to expel thewater of solution and convert the coating to an essentially waterinsoluble and water-repellant product, the solution of sodium carboxymethyl cellulose being applied to yield a driedcoating in the range offrom 0.1 to 0.4 pounds per thousand square feet.

8. The process of making adiaper having one side water-repellent whichcomprises applying to one side of a sheet of unwoven fibers having arandom distribution, a substantially continuous coating of a 0.5 to 2.0%aqueous solution of sodium carboxy methyl cellulose, applying heat tosaid coating on the order of 300 to 450 F. whereby a moisturetransmitting coating is obtained, applying to the other side of thesheet a substantially continuous coating of a 0.5 to 4.0% aqueoussolution of 25 to 40 parts of a solid poly- 75 ethylene glycol having anaverag molecular weight of 1000 to 7000 and 60 to 75 parts of anammonium salt 0! styrene-maleic anhydride interpolymer, and applyingheat to the latter coating on the order of 250 to 450 F. to expel thewater of solution and convert the coating to an essentially waterinsoluble and water-repellent product, the solution containing saidinterpoly mer being applied to yield a. dried coating in the range offrom 0.25 to 2.0 pounds per thousand square feet.

RAYMOND B. SEYMOUR. GEORGE M. SCHRODER.

10 nmmces ormn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Loomis Sept. 26, 1933 LeguillonDec. 3, 1935 Stoops July 20. 1943 Schwartz Sept. 28, 1943 Wallach Feb.18, 1947

